可变限速控制下的城市快速路交通流混沌分析

An Analysis of Traffic Chaos on Urban Expressways under Variable Speed Limits

可变限速策略是城市快速路交通系统中重要的管理手段,制定合理限速值需要考虑交通流运行特征与车辆速度特征因素。为更好地研究可变限速控制下的车辆行驶速度特征所引起的混沌现象,通过设定交通流中遵循可变限速值行驶车辆的不同比例p这一参数,以北京市三环快速路交通环境为背景,构建多种仿真情景得到速度时空序列,借助C-C法获得不同断面的速度序列时间延迟与嵌入维数,重构时间序列相空间,利用小数据量法获得最大Lyapunov指数即λmax,以判断混沌特征,并在相同流量下进行对比,分析发现,没有实施可变限速策略时,断面速度序列λmax为正;实施可变限速策略时,可变限速标识下游200m位置速度时间序列λmax为正,并且λmax与p存在二次回归关系,当p=76.8%时,速度序列λmax趋于0。以p为关键参数的分析结果可为制定可变限速值以及策略实施提供参考。

Variable Speed Limit（VSL）strategies have been used to manage traffic operation in urban expressway systems.To develop a reasonable speed limit values,the characteristics of traffic flow and speed should be taken into consideration.In this paper,traffic chaos on urban expressways is analyzed due to speed variation resulting from using VSLs.The ratio of vehicles complying with VSL in flow,p,is applied as the key parameter to analyze the speed characteristics.A section of 3rd Ring Expressway in Beijing is simulated using Vissim.The C-C method is used to reconstruct the phase space based on the speed time series data collected from Vissim scenarios.Small Data Set method is used to identify the traffic chaos by calculating the largest Lyapunov exponentsλmax.Traffic operations were compared between the scenarios with and without the implementation of VSLs.Analysis results showed thatλmaxof speed time series is positive without VSL,andλmaxof speed time series is also positive at the location 200 mdownstream of VSL sign and a quadratic regression model is found to fit betweenλmaxand p.The minimum value ofλmaxreached 0when p=76.8%.The results of this paper can be useful to support the decision-making of the speed limits and implementation of the VSL strategies.